Do I have the right to feel this way?

My SO’s mom bought a Louis Vuitton purse today and called and asked my SO can he give her half of what she paid for it. My SO agreed. Mind you i’m pregnant and can’t work because i’m due any day now so his income is what we’re relying on. I don’t even own a Louis Vuitton purse because they’re not in our budget. Whenever she asks for money for her shopping habit he gives it to her! Maybe it’s my hormones but I’m so frustrated and want to speak up about all this money he’s giving her, when we have a baby on the way. Should I say something, isn’t it my right to do so?